Titanium composite

ABSTRACT

A composite article comprised of at least two metallic layers. One of the layers being a metal from the group consisting of titanium and titanium base alloys and another being steel. The steel being a plain carbon steel having up to 1.5% of carbide former present in a carbide former-to-carbon ratio of from 1.5 to 25.

[ TITANIUM COMPOSITE [75] Inventor:

[73] Assignee: Allegheny Ludlum Industries, Inc.,

Pittsburgh, Pa.

22 Filed: Sept. 25, 1972 21 Appl. No.: 292,062

Joseph A. Chivinsky, Sarver, Pa.

[52] US. Cl 29/196, 29/198, 29/194, 29/199 [51] Int. Cl B32b 15/00 [58]Field of Search 29/198, 196.3, 196, 194, 29/199 [56] References CitedUNITED STATES PATENTS 7 2,137,945 11/1938 Mathesiiis 75/123 M 2,718,6909/1955 Ulam 29/l96.3 2/1956 Eckel 75/123 M 51 Dec. 17,1974

2,798,843 7/1957 S0lmi n.-. 29/198 2,906,008 9/1959 Boegehold 29/1982,908,966 10/1959 Wagner 29/198 3,015,885 l/1962 McEuen 297198 3,555,169l/l'97l Miller 29/1963 3,561,099 2/1971 Mizuharg.... 29/198 3,627,56112/1971 Richards 29/198 Primary 'ExaminerHyland Bizot Attorney, Agent,or FirmVincent G. Gioia; Robert F. Dropkin 57 ABSTRACT bideformer-to-carbon ratio of from 1.5 to 25.

7 Claims, No Drawings Titanium and titanium base alloys, hereinafterreferred to as titanium, are characterized by excellent.

corrosion resistance and a high strength to weight ratio, and hence, acombination of properties which makes them particularly desirable for anumber of applications. For example, their resistance to corrosion inchloride environments makes their use in heat exchangers, air pollutionequipment and marine equipment highly beneficial, and their highstrength to weight ratio makes their use in aircraft and otherstructural applications most advantageous. On the other hand, their highcost makes them economically unattractive at the present time.

One way to lessen the costs of parts and equipment made from titaniumand to thereby increase its usage is to use it in composites in which alayer of dissimilar and less expensive metal is sandwiched between-twolayers of titanium or between one layer of titanium and anothercorrosion resistant metal; e.g. stainless steel. A

particularly desirable dissimilar metal would appear to be plain carbonsteel. Plain carbon steel is relatively inexpensive and characterized bygoodmechanical prop erties. For example, it is a good heat conductor andwould not detract from titanium in heat exchanger applications. The useof plain carbon steel is, however, accompanied by potential dangers.Interstitial elements, carbon, oxygen, and nitrogen and particularlycarbon, can diffuse from plain carbon steel into titanium and especiallyinto the plain carbon'steel-titanium interface, and therebydetrimentally affect its properties, and particularly its ductility.Exemplifying this are 1 hard and brittletitanium carbides which form intitanium metal when carbon is present in amounts of approximately 0.15%and higher.

The present invention overcomes the potential .dan-

gers of using plain carbon steel in titanium composites by adding atleast one carbide former to the plain carbon steel. Carbide formers,such as titanium and columbium, have a high affinity for oxygen,nitrogen and carbon, and hence substantially preclude their migrationfrom plain carbon steel into titanium. Copending application Ser. No.000,177, filed Jan. 2, 1970, now Pat. No. 3,693,242 issued Sept. 26.1972, discusses the use of carbide formers in plain carbonsteel-stainless steel composites. It is accordingly an object of thisinvention to provide a composite article comprised of titanium or atitanium base alloy, and plain carbon steel containing a carbide former.

The article of the present invention is a composite comprised of atleast two metallic layers. One of the layers is a metal from the groupconsisting of titanium and titanium base alloys and another is steel.The steel is a plain carbon steelhaving up to 1.5% carbide formerpresent in a carbide former-to -carbon ratio of from 1.5 to 25. The termcarbide former refers to one or more of the elements which have a strongaffinity for carbon, and preferably to titanium and columbium. Theamount of carbide former is limited to 1.5% and preferably to 0.75%, asthe benefits obtained from further increases in the level of carbideformer are disproportionate with regard to the costs involved."

The ratio of carbide former-to-carbon in the plain carbon steel shouldbe between about 1.5 and 25. This means that the weight percent ofcarbide forming elements should be between 1.5 and 25 times the weightpercent of carbon. A minimum carbide former-tocarbon ratio of at least1.5 is imposed to insure sufficient carbide former to substantiallypreclude carbon. migration from the plain carbon steel toward and intothe titanium and topreclude the formation of enriched carbide areas,which are associated with decreased drawability. Composites formed fromplain carbon steel with carbide former-to-carbon ratios of 1.5 to 5 areoften preferred as they generally have higher yield strengths thansimilar composites formed from plain carbon steel with carbideformer-to-carbon ratios in excess of 5. On the other hand, compositeshaving carbide former-to-carbon ratios in excess of 5 are oftenpreferred as they are more workable than those'having ratios below 5.Yield strengths of the composites decrease and elongations increase withincreasing amounts of carbide former. An upper carbide formerto-carbonratio of 25 is imposed as the grain-size of the plain carbon steel canbecome undesirably large at higher ratios. A maximumcarbideformer-to-carbon ratio of 15 is often desirable since a range offrom 5-15 has proven to provide an optimum combination of drawabilityand cost.

In a particular embodiment, the article of the present invention iscomprised of a layer of titanium',.a layer of stainless steel, and. alayer of plain carbon steel containingcarbide former sandwichedtherebetween. Composites of this nature areparticularly desirable inapplications such as condensor tubes or heat exchanger tubes wheretheinner surface of the tube which is exposed to hot chloride solutionscould be titanium and where the outer surface which is exposed to air ordecontaminated water could be stainless steel. In such composites thecarbide former substantially precludes carbon migration from the plaincarbon steel toward and into both the stainless steel and titanium.

To further minimize carbon migrationanotherembodiment of the inventioncalls for a layerof barrier metal between the plain carbon steel andtitanium. The barrier metal is from the group consisting of nickel,cobalt, palladium, platinum, chromium and copper, as limited by thoseinstances wherein their melting point does not preclude their use.Although no criticality is placed upon the thickness of the barriermetal, layers ranging in thickness from 0.0001 to 0.005 inch arebelieved to be beneficial.

There are a number of methods for making the article of the presentinvention. These methods include: (1) pouring molten steel around orbetweensolid shapes of titanium and subsequently hot processing thecomposite as per normal mill methods for manufacturingv titaniumproducts; (2) compacting and sintering titanium powders on and to asteel surface; (3) pressure bonding; e.g. hot roll bonding, of titaniumto steel; (4) explosive bonding of titanium to steel; and (5) brazing oftitanium to steel. In all these methods care must be taken to providea.- nonreactive atmosphere, e.g. an inert atmosphere or a vacuum, toavoid surface contamination of the titanium as it is very reactive withox ygen and nitrogen at elevated temperatures.

The titanium alloy can be an alpha alloy; e.g. 5% A1, 2.5% Sn, balanceessentially titanium, an alpha-beta a1- loy; e.g. 8%.manganese, balanceessentially titanium, or

Metals Handbook, put out by the American Society for Metals, carbonsteel is defined as follows:

Steel containing carbon up to about 2% and other residual quantities ofotherelements except those added for deoxidation, with silicon usuallylimited to 0.60% and manganese to about l.65%. Also termed plain carbonsteel, ordinary steel and straight carbon steel."

It will be apparent to those skilled in the art that the novelprinciples of theinvention disclosed herein in connection with specificexamples thereof will suggest various other modifications andapplications of the same. it is accordingly desired that in construingthe breadth of the appended claims they shall not be limited to thespecific examples of the invention described herein.

1 claim:

1. A composite article comprised of at least two bonded metallic layers:at least one of said metallic layers being a metal from the groupconsisting of titanium and titanium base alloys; at least one of saidmetallic layers being steel, said steel consisting essentially of up to2% carbon, up to 0.6% silicon, up to 1.65% manganese, upto 1.5% carbideformer, balance essentially iron, said carbide former being from thegroup consisting of titanium and columbium, said carbide former beingpresent in a carbide former-to-car'bon ratio of from 1.5 to 25. i i

' 2. An article according to claim 1 wherein said carbide former ispresent in said plain carbon steel in a carbide former-to-carbon ratioof from L5 to 5.

3. An article according to claim 1 wherein said plain carbon steelcontains up to 0.75% of carbide former.

4. An article according to claim 1 wherein said carbide former ispresent in said plain carbon steel in a carbide former-to-carbon ratioof from' 5 to 15.

5. An article according to claim 1 having-at least two layers from thegroup consisting of titanium and titanium base alloys, and wherein saidlayer of plain carbon steel is sandwiched between said layers of metal 7from the group consisting of titanium and titanium base alloys.

6. An article according to claim 1 including a layer metal being fromthe groupconsisting of nickel, cobalt,

palladium, platinum, copper and chromium.

1. A COMPOSITE ARTICLE COMPRISING OF AT LAST TWO BONDED METALLIC LAYERS:AT LEAST ONE OF SAID METALLIC LAYERS BEING A METAL FROM THE GROUPCONSISTING OF TITANIUM AND TITANIUM BASE ALLOYS, AT LEAST ONE OF SAIDMETALLIC LAYERS BEING STEEL, SAID STEEL CONSISTING ESSENTIALLY OF UP TO2% CARBON, UP TO 0.6% SILICON, UP TO 1.65% MANGANESE, UP TO 1.5% CARBIDEFORMER, BLANCE ESSENTIALLY IRON, SAID CARBIDE FORMER BEING FROM THEGROUP CONSISTING OF TITANIUM AND COLUMBIUM, SAID CARBIDE FORMER BEINGPRESENT IN A CARBIDE FORMER-TO-CARBON RATIO OF FROM 1.5 TO
 25. 2. Anarticle according to claim 1 wherein said carbide former is present insaid plain carbon steel in a carbide former-to-carbon ratio of from 1.5to
 5. 3. An article according to claim 1 wherein said plain carbon steelcontains up to 0.75% of carbide former.
 4. An article according to claim1 wherein said carbide former is present in said plain carbon steel in acarbide former-to-carbon ratio of from 5 to
 15. 5. An article accordingto claim 1 having at least two layers from the group consisting oftitanium and titanium base alloys, and wherein said layer of plaincarbon steel is sandwiched between said layers of metal from the groupconsisting of titanium and titanium base alloys.
 6. An article accordingto claim 1 including a layer of stainless steel, and wherein said layerof plain carbon steel is sandwiched between said layer of stainlesssteel and said layer of metal from the group consisting of titanium andtitanium base alloys.
 7. An article according to claim 1 including alayer of third metal between said layer of metal from the groupconsisting of titanium and titanium base alloys and said layer of plaincarbon steel, said layer of third metal being from the group consistingof nickel, cobalt, palladium, platinum, copper and chromium.